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Temperature Dependence of MgATP and MgADP Affinity of Fast and Slow Rat Myosin Isoforms: An in Vitro Motility Assay Approach
No full textIt has been suggested that the rate of ADP release from acto-myosin and the rate of acto-myosin dissociation by ATP may play different roles to define unloaded shortening velocity of slow and fast myosins and tha their role might change with temperature (Nytray et al. 2006; Iorga et al. 2007). In this study, the in vitro motility assay (IVMA) approach was used to study the effect of MgATP and MgADP on actin sliding velocity (Vf) on slow and fast skeletal myosin isoforms at different temperatures. The velocity of actin filaments sliding on pure slow (myosin 1) and pure fast (myosin 2B) myosin isoforms from the rat was determined in a range of [MgATP] (0.01-2mM) and in the presence or absence of 2mM MgADP. Experiments were performed at 20, 25 and 35 °C. The rate constants of ADP release and ATP binding to acto-myosin were calculated. The inhibition of Vf by MgADP was greater in slow then fast isoforms and the rate constant of ADP release was higher in fast than slow isoform. The results suggest that, in slow isoforms, the maximum velocity could be limited by the rate of ADP dissociation from actomyosin. The ADP inhibitory effect decreased and the rate constant of ADP release increased in each isoform with temperature accounting for the increase in Vf. No differences were found between isoforms and among temperatures in the rate constant of ATP binding. The possibility that the rate of acto-myosin dissociation induced by ATP could play a role in defining Vf in fast isoforms will be discussed
Temperature dependence of MgATP and MgADP sensitivity of sliding velocity on fast and slow rat myosin isoforms
No full textHindlimb unloading induces changes in actin sliding velocity of mouse pure myosin isoforms
No full textDisuse muscle atrophy following hindlimb unloading (HU) can cause
changes in unloaded shortening velocity (V0) at muscle fiber level
(Zhong et al., 2006). The aim of this study was to clarify whether myosin
motor function can be affected by HU, accounting for the observed
changes in V0. The in vitro motility assay (IVMA) approach was used.
In IVMA the properties of myosin motor could be investigated in the
absence of other myofibrillar proteins by assessing actin sliding velocity
(Vf) on isolated myosin. Vf is widely considered analogous to V0 as
significant correlation between V0 and Vf was demonstrated (Canepari
et al., 1999). Pure type 1 myosin from soleus (S) and type 2B myosin
from gastrocnemius (GAS) muscle of HU and control (C) mice were
analyzed. The results show that Vf on myosin 2B from HU was significantly
slower (2.70 ± 0.32) then Vf on myosin 2B from C
(4.11 ± 0.35), whereas no significant difference was found for myosin
1 (0.84 ± 0.17 vs. 0.89 ± 0.04). The results suggest that type 2B
myosin motor could be functionally altered by HU. The effect could be
related to a differentMLCisoform composition (Zhong et al., 2007) or a
post-translational modification of myosin (Ramamurthy et al., 2003;
Coirault et al., 2007). Preliminary analysis of MLC composition show
no differences between HU and
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Novel Approach Applied to IVMA to Study the Modulation of the Actomyosin Interaction by MgATP In Fast Skeletal Muscle
No full textIn this study we used an “in vitro motility assay” (IVMA) approach to investigate the effect of the variation of [MgATP] in determining the number and the sliding velocity (Vf) of actin filaments moved by fast skeletal myosin. Vf was studied on type 2B HMM from rats at 25C°, 100mM ionic strength and at varius [MgATP], [MgADP] and [Pi]. We designed a new experimental set-up to perform experiments at lower ionic strength and in buffers that had no interference with the ionic environment, in order to mimic physiological condition. This set-up allowed a complete and chemical speciation of the solutions opening the possibility to perform an accurate thermodynamic study. Therefore, along with kinetic measurements also quantitative thermodynamics measurements were carried obtaining the ∈′′G of MgATP hydrolysistaking into account pH and [Mg2+]. We correlate the thermodynamics property of the system to Vf and to the number of sliding actin filaments which were assessed by a purpose-designed software. Preliminary results indicate: a) no straightly correlation between values of ∈′′GATPand the velocity of actin filaments, b) an increase in thenumberof sliding actin filaments at low [MgATP] and no changes when the ratio [MgATP] / [HMM] was kept constant c) a decrease in the velocity of actin filaments at [Pi]=30mM. More investigations are required to confirm the unexpected results that indicate a complex role of MgATP and its metabolites in the modulation of actomyosin interaction
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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